Radio frequency (RF) power amplifiers (PA) 120 with a fixed voltage supply (e.g., direct current (DC) power supply (PS) 112) can be most efficient at peak power, as illustrated in FIG. 1A. Efficiency of the RF PA can be worse at lower power levels. Thus, power amplifiers with a high peak-to-average (PAR) waveform (e.g. PA used in Mobile User Objective System (MUOS)) can be inherently inefficient. MUOS is an array of geosynchronous satellites developed for the United States Department of Defense (DoD) to provide narrowband (e.g., 64 kilobits per second (kbit/s) and below) connectivity for global satellite communications (SATCOM) for use by the United States and its allies.
Envelope tracking power supplies (ET PS) 110 can be used to improve energy efficiency of RF power amplifiers, as illustrated in FIG. 1B. An ET PS can replace a fixed direct current (DC) supply voltage 112 to the RF PA 120 with a dynamic supply voltage 142, which closely tracks an amplitude, or envelope of a transmitted RF signal 140.
Referring back to FIG. 1A, RF PAs can be supplied with a fixed DC voltage 112, but may only be energy efficient when the RF PAs are in compression (e.g., at the peaks of the transmitted waveform). Most of the time, the supply voltage 144 can be far higher than the transmission voltage 140 (or transmitted RF signal), and the excess power can be dissipated as heat 148 in the PA device. For example, with orthogonal frequency-division multiplexing (OFDM) signals up to 80% of the energy in the PA can be wasted (dissipated as heat).
Referring back to FIG. 1B, envelope tracking can work by dynamically adjusting the supply voltage 142 to the signal generated by the PA 120, which can maximize the energy efficiency (e.g., reduce the heat dissipation 146) of the PA by keeping the transmitted RF signal 140 in compression over a whole modulation cycle, instead of just at the peaks.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.